In most customary signal transmission systems, the line side component (connected to the transmission line) of both transmitter and receiver is electrically isolated from the operating side where a data signl for transmission either is present or will be received. Thus, the data transmission is guaranteed a high level of protection from interference. Consequently, the line side component of the transmitter and receiver of both transmitting and receiving stations must be supplied with voltage which is lso electrically isolated from the operating side.
It is customary to feed the operating side of the transmitter and receiver of both transmitting and receiving station with a supply voltage from the operating side and to feed the line side component of both transmitter and receiver via supply voltage lines that accompany the transmission line. The major disadvantage is that the supply voltage lines must be laid along the entire transmission route; consequently, installation costs increase significantly. A further disadvantage of this method of supplying power is that it is difficult to keep the supply voltage at least approximately constant along the entire transmission route.